Cummins engines
Cummins names can refer to different fuels, applications and emissions generations. Start with the full designation and engine serial number, then find the matching rating and documentation. The X15 diesel and X15N natural-gas engine are not interchangeable versions of one fuel system. This directory emphasizes truck applications; a marine, industrial or motorhome specification should not be applied to a road truck simply because the displacement looks similar.
Compare the model families
| Model / family | Application | Overview | Model notes |
|---|---|---|---|
| X15 | Heavy-duty diesel family | The X15 is Cummins’ heavy-duty diesel family, with different series and model-year offerings. Cummins distinguishes its Efficiency Series from other X15 configurations and separately describes a 2027 generation. A bare X15 badge does not identify the rating, emissions system or approved application. | Read the profile → |
| X12 | 12-litre-class diesel family | The X12 is a Cummins diesel engine family used in truck applications. Cummins’ truck body-builder material lists X12 separately from its larger X15 range. Its published ratings depend on the application and generation, so a fire-apparatus or motorhome rating should not be assumed to apply to a freight truck. | Read the profile → |
| L9 | Medium-duty diesel family | Cummins lists the L9 in its medium-duty truck range. The catalogue contains different model-year entries, including a 2024 medium-duty listing. L9 diesel should be distinguished from L9N natural gas; the similar name does not mean identical fuel, service or vehicle requirements. | Read the profile → |
| B6.7 | Medium-duty diesel family | The B6.7 is a Cummins medium-duty diesel designation. Cummins publishes truck-specific entries as well as other applications in its product range. Do not assume that a pickup, industrial or other B-series rating describes the commercial truck you are evaluating. | Read the profile → |
| ISX12N | Natural-gas truck engine | ISX12N is a Cummins natural-gas engine designation. Cummins’ body-builder catalogue includes a 2018 listing, and the company distinguishes it from its later X15N natural-gas offering. It must not be confused with an ISX diesel or treated as a diesel engine with a different fuel-price label. | Read the profile → |
| L9N | Natural-gas medium-duty family | The L9N is a natural-gas member of Cummins’ truck engine range. It appears separately from the L9 diesel in the manufacturer’s product listings. That fuel distinction affects the vehicle’s supporting systems and the way an operating-cost comparison must be assembled. | Read the profile → |
| X15N | Large natural-gas truck engine | Cummins’ X15N is a natural-gas truck engine, distinct from the X15 diesel family. Cummins lists ratings up to 500 hp and 1,850 lb-ft for this offering. These are published family maxima, not a statement that every installed engine has those ratings. | Read the profile → |
Bring the exact specification.
The family name helps organize your search. The build sheet, serial number and relevant manufacturer documentation identify what is installed. Compare like-for-like applications and request evidence for cost or performance claims.
Manufacturer references support the model facts. Our examples and comparisons are editorial interpretation prepared with AI assistance, not road tests or an expert inspection.
Check the year, market and exact build before applying a specification. This guide does not authorize parts fitment, repairs, modifications or loading.
Cummins manufacturer reference ↗Independent editorial resource. Brand names identify equipment; they do not imply a partnership or endorsement.